Chip attenuators are used in RF and microwave circuits to change signal level to act as buffers between amplifier stages to prevent oscillation, and for impedance matching for frequency selective devices such as filters or mixers. There are three typical constructions used to fabricate chip attenuators. Referring to FIG. 1, there is shown a top view of one type of a prior art chip attenuator 10, generally referred to as a "T" type chip attenuator. The attenuator 10 comprises a flat rectangular substrate 12 of an insulating material, such as a ceramic or plastic. On a surface 14 of the substrate 12 are first and second conductors 16 and 18 which are spaced apart. A third conductor 20 is on the surface 14 and extends between the first and second conductors 16 and 18. The third conductor 20 has a head 22 thereon at one end. A fourth conductor 24 is on the surface 14 and is spaced from and substantially parallel to the head 22 of the third conductor 20. A first resistor 26 is on the surface 14 and extends between the first and third conductors 16 and 20, and a second resistor 28 is on the surface 14 and extends between the second and third conductors 18 and 20. A third resistor 30 is on the surface 14 and extends between the head 29 of the third conductor 20 and the fourth conductor 24. Each of the conductors 16, 18, 20 and 24 are films of a thick or thin film conductive material, and each of the resistors 26. 28 and 30 are films of a thick or thin film resistance material. Thus, the "T" type attenuator comprises three resistors connected together.
Referring to FIG. 2, there is shown a second type of prior art chip attenuator 32, which is general referred to as a "Pi" type attenuator. Attenuator 32 comprises a flat, rectangular substrate 34 of an insulating material, having a surface 36. On the surface 36 are spaced first, second and third conductors 38, 40 and 42. Also, on the surface 36 are first, second and third resistors 44, 46 and 48. The first resistor 44 extends between the first and second conductors 38 and 40, the second resistor 46 extends between the first and third conductors 38 and 42, and the third resistor 48 extends between the second and third conductors 40 and 42. Thus, the attenuator 32 comprises three resistors connected in a series/parallel relationship.
Referring to FIG. 3, there is shown a third type of prior art chip attenuator 50, which is generally referred to as a "sheet" type attenuator. Attenuator 50 is similar to the "Pi" type attenuator 32 of FIG. 2 in that it comprises a flat, rectangular substrate 52 having a surface 54, and three spaced conductors 56, 58 and 60 on the surface 54. However, instead of three separate resistors, the "sheet" type attenuator 50 has a single resistance film 62 on the surface 54 and extending between the first, second and third conductors 56, 58 and 60. However, in essence, the single resistance film 62 forms a resistor extending between the first and second conductors 56 and 58, and a separate resistor extending between the third conductor 60 and each of the first and second conductors 56 and 58. Thus, the "sheet" type attenuator 50 provides the same resistor circuit as the "Pi" type attenuator 32.
The choice of which of the above types of attenuators is used depends on the desired power dissipation and frequency response. The "T" type attenuator 10 works well for attenuation values below 2 dB since the series resistors are larger and easier to fabricate. The "Pi" type attenuator 32 and the "sheet" type attenuator 50 work well for high attenuation value because the are two shunt resistors. However, a problem with all of these types of attenuators has to do with the small amount of inductance associated with the resistor geometry and connecting metal terminations. The inductance forms a series R-L circuit which behaves like a low pass filter. The effect of the inductance is a reduction in the attenuation with increasing frequency. The effect of the inductance on a "T" type attenuator 10 is much worse than on either a "Pi" type or "sheet" type attenuator. Therefore, the "Pi" type or "sheet" type attenuator is preferred. However, it would be desirable to further improve the performance of the "Pi" type, "sheet" type and "T" type attenuators.